On The Edge

The First Electronic Dive Computer

It’s ironic to consider that Dr. Bill Stone and his team were preparing to plumb the depths of Wakulla Springs using heliox, custom tables, souped-up electric scooters and Stone’s prototype rebreather, about the same time that the sport and scientific diving communities were grappling with the efficacy of the newly introduced dive computer. To wit:

The U.S. Navy tables prescribe a no-stop limit of 25 minutes for a 100 feet dive. So how can a dive computer say I have 15 more minutes?

Launched in January 1983, Orca Industries Inc.’s Electronic Dive Guide (EDGE)—the first commercially viable microprocessor-based dive computer1 which utilized a mathematical model, introduced the concept of multi-level diving, and in doing so helped revolutionize sport diving. The 1.6 pound, milled-aluminium, brick-sized EDGE included a unique graphical user interface (GUI), which showed the diver’s theoretical tissue loading in real-time, and enabled users to do full decompression dives to 200 ft./60 m.

The success of the EDGE, and dive computers in general, required considerable education on the part of both dive industry leaders as well as the consumer! Issues included the general mistrust of relying on electronics for underwater life support; the fear that increased bottom times would disrupt dive operators’ schedules, and result in more cases of decompression sickness (DCS). Furthermore, there was (were) a concern(s) that computers might encourage divers to go deeper and stay longer than they should.

The turning point came with the “Dive Computer Workshop” organized under the auspices of the American Academy of Underwater Sciences (AAUS) by then president Michael Lang and decompression guru Dr. RW Bill Hamilton of Hamilton Research Ltd. in September 1988. The workshop included manufacturers, hyperbaric medicine practitioners, and representatives from recreational, cave and scientific diving community. Together they collaborated and cleared the air regarding the potential dangers of dive computing, validated the concept, and created a set of 13 recommendations for their use.

Following the workshop, the opposition to dive computers withered; numerous new models were introduced, the technology dramatically improved, and dive computers became a standard piece of sport diving equipment virtually overnight. It would take nearly a decade more for the technology to be adapted for technical diving with the introduction of the VR Technology Ltd.’s VR3 in 1997, which could handle mixed-gas decompression.

I caught up with Richard Nordstrom, then CEO of Orca Industries to discuss the challenges of bringing the dive computer to market in 1989, the year that I prepared to launch my magazine “aquaCORPS Journal.” The original interview, which is shown below, ran in “Discover Diving” magazine in JAN/FEB 1990. That year, Nordstrom left Orca to become the CEO of Stone’s Cis-Lunar Development Laboratories Inc. (1990-2001) which commercialized Stone’s rebreather technology.

Several years later, I interviewed Karl Huggins, then manager of the Catalina Hyperbaric Chamber, who helped develop the EDGE software under Orca Founder and President Craig Barshinger. The interview, also shown below, was published in aquaCORPS Journal N6 Computing June 1993.

These interviews, which now date back almost a quarter of a century, reflect on the challenges of developing dive computer technology, and how industry perceptions about sport diving have changed.—Michael Menduno

Interview with Richard Nordstrom

JAN/FEB 1990:

On the EDGE: Two Hours with Richard Nordstrom

“Computers are useless. They can only give you answers.” Pablo Picasso

Every now and then, someone comes up with a revolutionary idea that changes the way people do things; the way we view the world. The electronic dive computer is a good example. Since their introduction in 1983, dive computers have impacted every facet of the industry, belying their current market penetration of 12-15 % depending on how you count the numbers. Most serious divers regard them as an essential piece of gear.

Any discussion of dive computers must include mention of Orca Industries. Founded in 1982 by Craig Barshinger and Jim Fulton—two men who set out with more vision and spunk than initial capital—Orca pioneered the dive computer with the introduction of the EDGE, the first commercially available diving meter that really worked. From a rocky start trying to convince people a computer wouldn’t kill them, in six short years the Orca EDGE has become a standard against which all diver computers are measured.

In retrospect, what Orca did was obvious. Obviously, the U.S. Navy Repetitive Dive Tables—a product of the Sputnik era—would be replaced by the computer.

But the company did more than simply embedding the mathematics of tissue calculus on a chip; they brought a whole new level of technical sophistication to diving, and with it a new freedom—akin to the impact of the Personal Computer on business. Orca put power and responsibility back in the hands of the individual diver, and in doing so, ushered the sport into a new era.

Orca has changed a lot of people’s perspectives – it certainly changed Richard Nordstrom’s. Recruited in 1986, to assist in putting the business on a more solid footing, Nordstrom was hooked when the headhunter on the phone asked, “Do you know anything about diving?" With an irreverent self-deprecating sense of humor that would put the most timid interviewer at ease, Nordstrom, 37, is visibly shy when thrust into the limelight, preferring to work behind the scenes whenever possible. When I spoke to him a month after our interview and told him the title I had selected for this article, he sounded a little distressed, ‘God, they’re all gonna say, I hope he jumps!’

Shy about himself, he is anything but when it comes to talking about his passions: diving and Orca, in that order. Ask him a question about diving techniques, history, technology, or about his experiences diving for 500 B. C. amphora in Sicily, at depths deeper than this magazine will print, (‘Don’t make it sound like I was raping and pillaging a lost continent!’), he will give at least four different perspectives, in rapid-fire succession. And just when he sounds finished he’ll pause for a second to laugh, pull out a favorite dive story —one of hundreds—to illustrate his point.

Hardly a newcomer to diving, Nordstrom’s first scuba experience came in 1961, cleaning the pool, at the Marine Base where his father was stationed. It was an experience that kindled a fascination, maybe a calling, that has driven him ever since. In the early, heady days of New England diving, when a diver forgetting his wetsuit—it was “his” in those days—would eagerly plunge into the frigid water, sheer enthusiasm overcoming the cold, Nordstrom was never out of his element. Contract diver, Ph.D. student in Marine Ecology, a NAUI instructor, he taught classes in underwater research at the University of Connecticut, lectured at the Boston Museum of Science, and spent his “free time” running dive trips from Nova Scotia to Key West. Turned on to diving, Nordstrom added a twist to the popular sixties campus slogan, “Tune In, Turn on and Drop Down.”

In 1978, at the urgent plea of his best friend, Nordstrom shrugged off the comfort and promise of a budding teaching career, packed up his dive gear and a wary new wife, and moved to the Turks and Caicos Islands’ Pine Cay—a tiny, pristine island under British Crown Rule—to help run a struggling marine charter operation. Though never really designed to make money, Nordstrom made Meridian Marine a business.

After two years, perhaps influenced by the movie The Graduate (“What are you going to do with your life, Benjamin? … glug …glug..glug”), opportunity washed up on the beach, in the form of a plum job with Arbonite Corporation, a Pennsylvania-based plastics manufacturer—the wave of the future. Arbonite successfully lured Nordstrom from his island hideout, and in six years, he worked his way up from Manager of Dip Molding to Executive Vice President. Ironically, one of the divisions that he started to supply plastics to the emerging scuba industry, built the first holster for the EDGE. Two years later he left to join the computer’s inventors.

In years to come, the EDGE will probably be regarded as a classic like the Corvette, the Levi jean, or the first hand-held HP scientific calculator. But Orca is not in danger of being relegated to the annals of diving history any time soon. With the introduction of their newest dive computer, the Delphi, Orca has demonstrated a penchant for remaining at the cutting edge of technology. With Nordstrom at its head, it will probably stay that way for a long time to come.


Menduno: Is dive technology changing the way people dive?

Nordstrom: Definitely. Technology has always been a driving force in our industry whether you’re talking about the aqualung itself, the submersible pressure gauge, or the buoyancy compressor, you name it. All of us involved in dive computers believe they will help develop a new freer spirit in diving and enable divers to enjoy this unique environment in a more relaxed manner with less anxiety. We’re making it easier for people to dive and that’s going to bring more people into the sport.


Not everyone agrees with your assessment.

Well, there are opponents of dive computers who say they’re creating potential danger by making it easier for people to go where they shouldn’t. Perhaps that’s true. That’s why it’s important that the educational groups; PADI, NAUI, SSI, the YMCA and others, insure that education keeps pace with diving technology.


Do you think additional education or certification levels are needed?

I think so. You see it all the time, particularly on liveaboards and dive charters where people have to do their own planning. Divers climb out of the water and walk over to each other, pull out their dive tables and get a glazed look on their faces. “I haven’t done this in two years.”

“I thought you knew how to do it.”

“No, don’t you?”

“Let’s look around.”

One out of ten people have a computer on board with them and of the nine remaining, four or five will be struggling with the tables.


I understand that Orca’s new Delphi computer has a working depth of 300 feet, where the EDGE and Skinny Dipper only function to 200 feet. How do you reconcile that with the recreational diving guidelines limiting dives to 130 feet?

First of all, the Delphi Pro is a commercial product specifically designed only for qualified commercially trained divers who find themselves in situations where they may have had to drop below sport diver limits for commercial reasons. These people understand the risks, are trained to deal with them, and have support facilities to assist them when there are problems.

With either model, the sport diver can feel comfortable that he or she is buying an instrument with a lot of functionality.

Again it goes back to the basics of common sense. Just because the speedometer on your car goes up to 155 mph doesn’t mean that you should drive that fast, or that you are qualified to do so. The fact is, there is a market demand for increased capability. That’s the American side.

European diving is very different. People generally dive much deeper and also do decompression diving as part of their diving format. PADI and the U.S. agencies have always stressed non-decompression diving here in the states, but in Europe you’re talking about a very different culture, and a different approach to the whole thing. The European diver is very independent.

You’re providing the basic technology and people are going to adapt it to their own needs.

That’s right. Dive computers, like any other instrumentation, provide data and information, which has to be interpreted and used intelligently. It’s a guideline —you have to decide what to do with it. Different people are going to interpret and use the guideline differently.

There is a certain amount of conformity, which we have to strive toward—yet we all have a free spirit of adventure, which allows us to dream. It’s part of being an American. That’s why we are not ants and we are not cattle. We are homo sapiens, people, human beings. It’s what makes us unique and so special. Not just here on Earth, but to the Universe—because we’re going to get out there some day.


Let’s talk a little about the early days of Orca, before you joined the company. Was it difficult to convince the diving public that computers made sense?

Orca was founded by Craig Barshinger and Jim Fulton, two young bucks who set out with an idea and did an incredible job. You see, Orca spent the first part of its life, actually an incredible amount of time and energy trying to convince people to use their computer. ‘Try it. You’ll like it. It won’t kill you.’ Here we had the U.S. Navy Tables—God’s Gospel Truth, like Moses coming down from the mountain, with tables carved inn stone: “Thou Shalt Not Stay Down Longer Than 60 Minutes” And suddenly you had this computer saying you could stay down for “another twenty minutes.” It was tough.

The amazing thing, which most people don’t realize, was that the U.S. Navy Repetitive Tables were only tested on a total of about sixty repetitive dives. That was it. When you learn about statistics and population ecology, you realize, you don’t make decisions based on sixty samples of data. That may be all you have to work with, but the Navy certainly had the ability to expand that. Now they have millions of controlled dives, but their initial experimentation was given the blessing based on a very small number of dives. Fortunately the tables work—they do work—for most people.

Eventually, Craig and Jim, and later Karl Huggins, from the University of Michigan, brought out the EDGE—the first commercially viable decompression computer that really worked. It was a stroke of genius, and I think, they deserve a special place in heaven for what they did. The computer’s algorithms were Haldanian-based, just like the Navy Tables, and the simplicity of it was so natural: “If you’re not at the bottom the whole time, you’ve ascended and the pressure is reduced, you should get credit for it.” Like a lot of laws in physics, and the other sciences, it was a simple idea—almost obvious in retrospect—but one with very powerful implications.

That’s one thing I like about Orca, we’ve always maintained simplicity and intuitive design—what’s simplest for the diver.


Dive computers have become accepted as a viable, even an essential, technology. What are some of the issues that computer manufacturers are working to address?

Well, one issue that’s starting to raise its head is “Whose model is the best? Whose model is the safest? How safe is safe?

It’s a big problem, because there’s no such thing as absolutely safe, each of us are all so different physiologically and metabolically. The only way you’ll never have to worry about decompression sickness is if you never dive or never fly. Then all you have to worry about is the threat of thermonuclear war, a real explosive decompression situation!

Right now, there are several algorithms on the market. There are the Haldanian models, the Merrill-Spencer modification, the Swiss Buhlmann and the modified Swiss Buhlmann; some of them are sea level models, others are high altitude based. Most manufacturers have chosen one model and tweaked it for various reasons. They use words like, “Ours is more conservative.” But that’s like saying ours is safer. They are marketing points that are being driven home to consumers. But the real issue is: “What is safe-- how do you measure it?”


How will the question get answered?

It has to start with the consumer. There are a lot of self-proclaimed experts out there, people who may be deeply involved in the sport but don’t necessarily have the tools to be a real expert. They may present well, and a neophyte to the whole area may think, “My God, this guy really knows what he’s talking about,” when he may not. There’s a simple question to ask to find out i.e. Let me see the data. Let me see the tests. Let me see the facts!

Surprisingly, many consumers don’t ask this. They need to ask more. That’s part of the educational process. We want people to know the facts. We’ve had tests run out of the Catalina Chamber. We have over 3,000,000 dives on our computers, and we keep track of a lot of the information. We’ve sent out literally tens of thousands of questionnaires and run Doppler studies for the last two years in open water; Doppler studies on people using our equipment in multi-level, multi-day, repetitive diving. We’ve also come out with a safety pamphlet that’s received a lot of industry support. It basically tells you right up front, ‘You can get hurt using this instrumentation; but here’s how you use it with common sense.’ We’ve taken a leadership role on the issue of safety and computer technology, but much more needs to be done by the diving community as a whole.


Like what?

Well, until fairly recently, there wasn’t a successful coordinated effort to really analyze diving injuries. Diver's Alert Network (DAN) is changing that and they should get a lot of credit for what they’re doing. The bottom line is we finally have a focal point to find out who was bent, why they were bent, and what actions led to it. That’s how we learn.

We’re just at the beginning, and unfortunately, there hasn’t been a lot of money in the scientific community, NIH or NSF, for diving research. We need to find people and organizations, which will help support, finance and do the real bang-up scientific studies that are necessary to find out what’s going on in our industry.


Do you think the industry will ever agree on a standard decompression model?

I don’t know. A lot of people have said we should move to a new standard. People in the industry are so used to having God’s Truth—the Navy Tables—that they’re uncomfortable without a set standard, but I don’t know if we’ll ever be able to come up with one. A lot of divers aren’t going to fall within any one standard and I think it would be very difficult to determine what a safe standard is. No one can define it.


It’s a good issue, because I know there are divers who say, “Well, I’m diving with the XYZ computer because it gives me ten minutes less bottom time than the EDGE on ‘this kind of dive’.” Less bottom time! Is that good? Is that bad?

It depends. There’s a bell shaped curve for the population: every model assumes one. And there are always people who are going to fall outside the parameters of the curve. You can make the model more conservative by increasing the curve, but at what cost does it increase? All those people who fell near the center of the curve may be paying extremes for those on the outside. One solution would be to settle on a couple of different models, which offer different degrees of ‘conservatism.’


Do you foresee computers becoming more “application-based”, for example, models for specific types of diving like high altitude or decompression or for different diver profiles?

Suppose you had an EDGE, and in ten years you realized, ‘Gee, I’m not the big athlete I used to be. I want to be more conservative. Today, you could take your EDGE and you could dive it more conservatively very easily. It’s not difficult because it’ll give you the information you need to do that. But suppose you don’t even want to have to consider what conservative is.

Now suppose your EDGE had a button on the side, and by clicking it, you could change the ‘M Valve’<1>, and make the model more conservative. Twenty years from now, you’re 70 years old. You’ve retired and only dive every couple of weeks. You’re fortunate to have a friend who drags your tanks down to the water for you, and you sort of roll into your gear and go diving. ‘Click.’ You push the button and go to the next setting.

Or maybe, you’re going to be doing some pretty deep dives this weekend, and you want to be even more conservative than usual and have an additional margin of safety. All you’d have to do is click your EDGE. I use the word more conservative versus conservative. They’re relative terms. That’s one idea.

The ideal situation, of course, would be to stick a catheter in your arm and measure partial pressures of gases in the bloodstream while you’re diving. But most divers would tend to get a little upset watching the blood being pumped out of their arm while they’re swimming around. In fact, even the instruments that do the measurements would probably make most people nervous.

Eventually, there will probably be actual tests that divers will be able to take to determine a general profile of their reactions to depth and pressure. Perhaps they’ll go into a chamber as part of their course on dive computers and will be run through a series of dives, and monitored physiologically to get a feel of where they are on the bell-shaped curve. It may even go to the extreme of giving some blood and tissue samples. I don’t think we’re really at the point where biopsies will be taken of all the various tissues in our body for partial pressure studies.

I’m not ready to volunteer for that. But through further research, there may be studies that can be performed on blood and tissues, body fat content, weight and so forth to indicate an individual’s susceptibility to decompression sickness and they’ll be able to modify their computer and diving accordingly.


Let’s talk about some of Orca’s products. Why don’t we start with the Delphi.

It’s the most wondrous instrument ever created, designed to benefit all of mankind.


Oops. Let me pause for a commercial break here. Did you say you’ve also been an evangelist?

Well, actually….


I understand you have just started shipping the Delphi. What would you say is the real breakthrough? Is there one?

The real breakthrough in Delphi in my mind, the excitement if you will, is what it’s going to be able to contribute to the diving community data-wise. This is an instrument that can be plugged into a special optical scanner, and dump a profile of its last 35 hours underwater in two and half minute increments, including: maximum depth and time, ascent and ceiling violations, all into a PC, in an ASCII file format. The data will be stored in the unit and pumped out through the LED display, which will be read by a scanner.


Will I be able to do that on my PC?

You will if you can afford the optical scanner, but it won’t be cheap. What we plan to do is offer an Annual Performance Check (APC). We’re asking everyone to ship their instrument back to us once a year to check its calibration and for a general maintenance check.

When a unit comes in, we’ll download the data, perform the APC and then send them a hard copy of their data along with the unit. The ASCII files will be sent to DAN who will become a treasure trove of the data, which at that point will be available to everyone.


That’s exciting!

I think so. We’re volunteering the data to DAN for two reasons. First, we don’t want to be the repository of raw data. We don’t want anyone to think we’re tinkering with it.

Second, is that DAN is in an ideal position to take the data, interpret it and make it available to others. The data is the most significant aspect of Delphi. Our marketing people say there’s a lot of other significant things, but as a scientist and a person interested in the future of diving, I think having that kind of data offers incredible potential.


Discover Diving is planning to do an in-depth product review of the Delphi, so I don’t want to take up our time discussing specific features. But there is one issue I’d like to talk about, and that’s the reliability of digital pressure gauges and the wisdom of mating them with the computer. I know it’s an issue on a lot of divers’ minds.

It’s a real important issue. There are basically three ways an instrument, like the Delphi, can become nonfunctional, and we’ve spent a lot of time and resources addressing each one of them in our design and testing. That’s one reason the computer didn’t come out when we originally wanted it to. We felt it was important to add a substantial number of additional reliability and time tests.

The first issue is a dead battery. We’ve designed an extensive series of forewarnings to alert the diver to a low battery condition. In the event of a low battery or outage, the Delphi allows a battery change without dropping any data. It also tells the diver, whether or not the battery charge was successful. We wanted to make it easy.

A second source of reliability concern is physical damage to one of the electronic components, for example, a transducer. We’ve designed the Delphi so that all of its electronics are ‘compartmentalized.’ It’s the same approach that is used on military aircraft and naval hardware. Think of it as a dive computer mated with a separate high-pressure system, which operates independently. The bottom line is, if one part of the system is knocked out, the rest of the system is still functional.

A final potential problem would be a failure in the microprocessor itself, a highly unlikely event. But let me stress: an instrument is an instrument. That’s why redundancy is so important in diving. In the case of the recreational diver, your buddy is your backup. And you always have the option of aborting your dive.

Professionals, like commercial divers and people doing specialized tasks, have backup and support systems built in. Right now, we’re looking at adding the ability, in the future, to mate an analog SPG as a backup for the Delphi, for special applications, where they are needed.

You know, the interesting issue about all of this is the misconception that the analog gauges we’re used to are really reliable.


I’ve had one go out on me and seen several explode.

Exactly, I’ve seen dozens explode.

It would be very interesting to measure and compare the MTBF (Mean Time Before Failure) between analog and digital gauges.


It would indeed. Overall, electronics are a lot more reliable than analog devices, because they function as a static design. Analog devices are based on a dynamic mechanical design and therefore are influenced and affected by many more outside variables.

They are also notoriously inaccurate, something on the order of ± 10-15 per cent, particularly after they have been banged around. With digital gauges, divers are going to be able to see in very finite terms how much air they are really consuming.


What about my EDGE? I have to confess I think I’ve grown addicted to it. Am I going to have to wean myself off of it?

The EDGE is still considered by many the premier dive computer on the market. It provides a quick graphic representation of what your tissues are doing. All the pros and the experts feel very comfortable with this format. After you’ve dived with the EDGE for ten or fifteen dives, you begin to realize just how much information is really there.


You just look at the graph.

Right. You begin to get quick, gross recognition of exactly what’s going on and it helps you to very easily plan your dive, while you’re diving. I don’t recommend that. I always recommend, ‘Plan your dive, dive your plan’; but then you have format within that that allows for flexibility. That’s what good diving is all about. God bless the EDGE owner!


So tell me, in ten years, what will my dive computer look like?

Ten or 15 years from now, it could be as long as 15, we may have the type of computer system that controls a lot more than your decompression status. We will probably have an integral computer system that electronically controls your regulator. It will be adjusted so that no matter what position you move in, it’s easy to breathe using electronic sensing devices.

We may end up with a single-valve regulator. Remember the original single-valve regulators? In the future, we may have a one-stage regulator that is electronically controlled to provide a lot of air or a tiny bit of air, just what you need. The same computer that’s running that regulator will be maintaining your decompression status.

You'll be able to enter your physiological profile into the computer and then program it to the degree of conservatism you want. There’ll also be an internal guidance system, which is part of it. You’ll jump in the water, go to the bottom of the anchor line and push a button on your inertial guidance system. That way no matter where you go, you’ll have a beacon—not a homing beacon, but an inertial system that will tell you, ‘The anchor line is that way.’

I think there will also be masks with heads-up displays—they’re not as sophisticated as you may think. The armed forces have them on canopies of aircraft, but there’s nothing directly for the individual that’s practical yet. It would require a huge helmet. But in five to ten years it’ll be there—a projection type heads-up display system, which focuses right into the retina of the eye. You will have an imaginary series of numbers right here—actually all the information you need—that can be clicked on or off, but you’ll be able to see through them and maintain a depth of field capability.


How will communications going to fit it?

Underwater communications are also going to become an integral part of the computer. A lot of people like being underwater because it’s quiet and serene. I like that too. But from an instructional and scientific viewpoint, communications are here to stay and it’s really exciting.

But communications is more than just talk: communications involve knowing where the divers are, how deep they are, and monitoring their vital signs. It won’t just be the astronauts who will have their heartbeats sent back to Earth; divers are going to be monitored. If anything happens in an unusual physiological sense, alarms will go off, letting surface people know this guy, at this specific location, is having a problem. I think it's inevitable.


Reprinted from “Discover Diving” JAN/FEB 1990


Interview with Karl Huggins

Huggins on EDGE

Karl E. Huggins, who helped develop the EDGE, is recognized as one of the pioneers of modern dive computers and doppler monitoring. He is currently the Director at USC Catalina Hyperbaric Chamber.


Menduno: You were one of the developers of "The EDGE." Did you foresee that DCs would become such a broad-based tool?

Huggins: There were some people who believed everyone would have a computer. From my perspective, I saw it as more of a high-end tool for people who were doing multilevel diving. It would give them the ability to continuously calculate their decompression in comparison to the table-based multilevel diving that was being done at the time.


What was your involvement?

What I did was to take a look at the recommended limits that Spencer, Bassett and Pulmonis had published on the basis of doppler studies and implemented them in the computer. One of the things that I was adamant about was testing to make sure the algorithms weren't way off base with respect to multilevel diving.


No one had applied the algorithm to multilevel profiles?

Not in a rigid, scientific type of study. There were a lot of people in the Caribbean "stepping up" the tables or reading them sidewise. In fact, tables were being used in a way they were never designed for and in some cases the profiles people were doing were probably violating the underlying algorithm. I was concerned about it. That was in the days when I thought the models meant something.


How do you view models now?

Models are basically an approximation to come up with a low risk profile. All of them carry a certain degree of risk. They're not written in stone and there are a lot of day-to-day physiological factors that simply cannot be programmed into a computer.


What is your view of the trend towards statistical-based approaches such as maximum likelihood analysis?

I see it as a trend, but there needs to be a caution with the acceptance of any type of algorithm. For example, if you look at Haldanian-based algorithms, you can design something that will work real well within a certain depth and time envelope. However, if you take the same algorithm outside of that envelope, it may fall apart. When you're looking at the statistical models, you've got to realize that their predictions are based on a series of historical data. The data is used come up with a best fit—the best model to predict what occurred. As long as your diving fits the data that was used to generate the model, then you'll have a relatively good fit. If you move outside that area, then it may not be as good of a fit in terms of prediction.


How did you approach that problem with the EDGE?

The EDGE was designed for people who were doing multilevel profiles. At that time, a typical profile might involve going deep for a short period time, ascending and spend most of the remaining time at shallow depths. That's how we geared our doppler testing; a deep multilevel dive at the beginning of the day, short-surface interval and then a shallow dive. A typical two-tank Caribbean dive.


How many test dives did you do?

Depends on how you want to count dives. If you look at the entire series as a dive series, then you can say that we did 12 dives because we had 12 different series. If you want to look at each one of the dives as an individual entity, then we had 119-person-dives.


In your mind what have been the major innovations in dive computers since the EDGE?

In terms of progression, I think there have been four major things. The first was probably ascent-rate warnings which I feel has been a very important feature. Secondly was miniaturization. Once there's a market you can invest in the miniaturization techniques. The third innovation was the ability to record the profiles and dump them back out to the user in order to be able to get an idea of what the actual profile was like. The fourth was being able to sit down communicate back and forth on a PC and be able to change various variables within the unit.


How about the next generation?

I'd like to see the ability to stick in safety factors. The one thing that I'm still concerned about with regard to dive computing is the amount of testing done. I don't know if there is any dive computer manufacturer out there… Let me restate that and put this in bold letters. I challenge any of the dive computer vendors to offer their algorithm for public inspection, and produce the actual test results that were carried out on the algorithm. What has happened is that companies have taken an algorithm, say the Bühlmann algorithm, and they've said, ‘Bühlmann has tested this model. We're going to tweak it and make it a little bit more conservative, stick it in our computer and say, OK, the testing associated with this computer can be traced back to Bühlmann.’


By default the algorithm is ‘tested!’

Exactly. And they haven't been! Because of that, I encourage people not to test the algorithm by pushing it to the outside envelope. I encourage them to back off. The real problem is that we don't really know how the general diving population are using their computers i.e. the profiles they're diving. What's more is that we have no denominator in any of our calculations. Whether we're trying to predict diving safety or anything else; we don't know what dives are being done. There's a lot of hand-waving being done to come up with figures.

I think there should be a large effort on the part of the manufacturers to support doppler or look at trying to set up a system like that proposed at the UHMS workshop on table validation ("Validation of decompression Tables," Undersea and Hyperbaric Medical Society, 74 (VAL)1-1-88, 1989). If we can start getting good profile information out of the field, then we could get a handle on the problem. I look at dive computers as an information-gathering tool.


Switching subjects a little, what do you think about the new desktop compression packages that have just come on the market?

It boils back to something that was said to me by Dr. Ed Thalmann of the U.S. Navy almost 9 years ago. I took offense at it at the time but over the years have gradually come to realize was a legitimate statement. I was presenting a paper at a UHMS meeting on computer-generated emergency exit tables for hyperbaric tenders. Thalmann came up, looked at it, and basically said, "Any idiot with a computer can create a set of tables." After my ears stopped burning a year or so later, I started thinking about it. It's true. Anybody who has a simple exponential equation and a computer can create a set of tables. You can do it with a spreadsheet if you want.


We have an article planned in an upcoming issue telling our readers exactly how to do it.

The exactness of the numbers can be intoxicating. But there is a big difference between precision and accuracy. The concern I have with the computers, whether it be underwater computers or desktop software, is that all they do is crank numbers through a simple mathematical equation. Unless you have some sort of data to back up what you're doing, you're just sort of shooting out in the dark and don't know what's going to be happening. You're not diving the original algorithm, you're testing a particular variation because you had to make assumptions to create this new set of tables.


What advice would you offer to people who are considering buying these programs?

Get as much information on the history of the specific algorithm and how it was tested. And don't be surprised if it's tough. I've been trying for years to get a handle on the algorithms being used in the testing that's been done on them.


The aftermath: Orca was acquired by EIT Inc., in the 1991. The electronics design and production services firm retooled Orca’s product line, added some new models and eventually stopped production of the EDGE. In 1999, EIT decided to withdraw from the diving market and discontinued its dive computer products.

[1] Introduced the same year in Europe, the Divetronic AG DecoBrain was a table-based lookup decompression device.


Written by Michael Menduno

Michael Menduno is an award winning reporter and technologist who has written about diving and diving technology for more than 25 years and coined the term “technical diving.” He was the founder and publisher of "aquaCORPS: The Journal for Technical Diving" (1990-1996), which helped usher technical diving into the mainstream of sports diving, and organized the first Tek, EUROTek and AsiaTek conferences, and Rebreather Forums 1 & 2.